Cosmic Background Explorer/DMR

Product Name
Sky Maps
Coord. System
Galactic or Ecliptic
Projection Type
COBE Quad Cube
Beam Size


There are six sky maps, corresponding to the two independent channels (designated A and B) and three frequencies (31.5, 53, and 90 GHz) of the COBE Differential Microwave Radiometers (DMR).

The maps are quadrilateralized spherical projections in either ecliptic or Galactic coordinates. A sparse matrix least squares minimization technique was used to derive, from highly redundant sky sampling, a differential temperature for each of 6144 map pixels while simultaneously allowing for instrumental and systematic effects.

The observations were made with a 7 degree beam and are presented in 2.8 degree pixels. The maps are in FITS files formatted as described in the DMR Explanatory Supplement.

File names indicate the frequency, channel, and world coordinates of the map (ecliptic by default; Galactic if specified). For example, the 53 GHz, channel A map in ecliptic coordinates is named dmr_skymap_53ghz_a.fits and its Galactic coordinate counterpart is named dmr_skymap_galactic_53a.fits.

Due to the differential nature of the observations, the maps have unconstrained antenna temperature zero points. While the dipole anisotropy has been removed to first order (see note above), emission from the Galaxy remains. The DMR Analyzed Science Data Sets include Galactic Emission Maps and Cosmic Emission Maps. The latter result when the Galactic emission is removed. The modeled Galactic components are synchrotron emission (dmr_synch.fits), free-free emission (dmr_free.fits), and thermal dust emission (dmr_dust.fits). Two techniques were used to produce the Cosmic Emission Maps, a "subtraction technique" in which the Galactic components are subtracted from the DMR maps (dmr_dsmb.fits), and a "combination technique" in which a linear combination of the DMR maps is used to cancel the Galactic emission (dmr_dcmb.fits). Corresponding to each of these maps is an equivalent map pixelized in Galactic coordinates (e.g., dmr_dust_galactic.fits). For a more detailed description of the Analyzed Science Data Sets and the corresponding Galactic Coordinate Data Sets, see the DMR Explanatory Supplement and references therein.

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Goddard Space Flight Center, National Aeronautics and Space Administration
HEASARC Director: Dr. Alan P. Smale
LAMBDA Director: Dr. Eric R. Switzer
NASA Official: Dr. Eric R. Switzer
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